How to become a Levite
First you must get clean. Here's how to do that:

Get sprinkled with water

Shave off every hair on your body

Wash your clothes

And the Lord spake unto Moses, saying,
Take the Levites from among the children of Israel, and cleanse them.
And thus shalt thou do unto them, to cleanse them: Sprinkle water of purifying upon them, and let them shave all their flesh, and let them wash their clothes, and so make themselves clean. Numbers 8:5-7

Next, find a young bull for a meat offering, along with some flour mixed with oil; and another young bull for a sin offering.

Then let them take a young bullock with his meat offering, even fine flour mingled with oil, and another young bullock shalt thou take for a sin offering. Numbers 8:8

Then go to the tabernacle and ask everyone to put their hands on you, while they offer you to the Lord.

And thou shalt bring the Levites before the tabernacle of the congregation: and thou shalt gather the whole assembly of the children of Israel together:
And thou shalt bring the Levites before the Lord: and the children of Israel shall put their hands upon the Levites:
And Aaron shall offer the Levites before the Lord for an offering of the children of Israel, that they may execute the service of the Lord.
Numbers 8:9-11

Next, you and your fellow Levites put your hands on the heads of the young bulls and kill them; one for a sin offering and the other for a
burnt offering.

And the Levites shall lay their hands upon the heads of the bullocks: and thou shalt offer the one for a sin offering, and the other for a burnt offering, unto the Lord, to make an atonement for the Levites. Numbers 8:12

This ceremony will show everyone that you and the other Levites belong to the Lord. [After God killed every Egyptian firstborn, he decided to make every
firstborn Israelite his own, but he changed his mind about that a while back (See Commandment #330) when he replaced every firstborn Israelite with the Levites. That way God won't have to kill all the Israelites when they come to the sanctuary.]

And thou shalt set the Levites before Aaron, and before his sons, and offer them for an offering unto the Lord.
Thus shalt thou separate the Levites from among the children of Israel: and the Levites shall be mine.
And after that shall the Levites go in to do the service of the tabernacle of the congregation: and thou shalt cleanse them, and offer them for an offering.
For they are wholly given unto me from among the children of Israel; instead of such as open every womb, even instead of the firstborn of all the children of Israel, have I taken them unto me.
For all the firstborn of the children of Israel are mine, both man and beast: on the day that I smote every firstborn in the land of Egypt I sanctified them for myself.
And I have taken the Levites for all the firstborn of the children of Israel.
And I have given the Levites as a gift to Aaron and to his sons from among the children of Israel, to do the service of the children of Israel in the tabernacle of the congregation, and to make an atonement for the children of Israel: that there be no plague among the children of Israel, when the children of Israel come nigh unto the sanctuary. Numbers 8:13-19

The working age for Levites is 25 to 50.
God set a mandatory retirement system for Levites. They must retire when they are fifty years old.

And the Lord spake unto Moses, saying,
This is it that belongeth unto the Levites: from twenty and five years old and upward they shall go in to wait upon the service of the tabernacle of the congregation:
And from the age of fifty years they shall cease waiting upon the service thereof, and shall serve no more:
But shall minister with their brethren in the tabernacle of the congregation, to keep the charge, and shall do no service. Thus shalt thou do unto the Levites touching their charge. Numbers 8:23-26